The present invention relates to an ascultation apparatus, i.e. an apparatus for listening to sounds from the internal organs of a living body, preferably the heart, respiratory or circulatory organs of a human, in particular to be able to analyse the sound in a more detailed manner for diagnostic purposes. The apparatus is intended to increase the possibilities for correct diagnosis for e.g. a doctor, by providing more detailed and specific sound information than what is possible when using e.g. an ordinary stethoscope, and the apparatus also provides options for recording, processing and displaying different characteristics of the captured sound.
Various types of xe2x80x9celectronic stethoscopesxe2x80x9d are previously known: From international No. WO 87/00145 (=SE 452,946) is known a means for monitoring respiration of infants, with microphones attached to the neck of the child. Each microphone is followed by a preamplifier, a bandpass filter and further amplifying and signal processing equipment. However, a real loudspeaker device for listening to the sound is not included, instead there are various types of warning equipment for giving a signal if a certain type of sound does not appear for a certain period of time. The function of the bandpass filter is to remove irrelevant frequencies, and the relevant and permanently set pass range is 300-1000 Hz when respiratory sounds from a small child are monitored. Thus, this previously known device is specially designed for one signal function, and it cannot be used in the type of comprehensive analysis which is the goal of the present invention.
From U.S. Pat. No. 4,220,160 is known an electronic stethoscope including a microphone and amplifying and processing equipment which lead to a loudspeaker for listening to processed sounds, as well as to other recording equipment. This is a system for transposing or converting the sound in such a manner that e.g. very low frequencies (25-75 Hz) are shifted to frequencies above 250 Hz, which frequencies are more easily audible and also easier to transmit e.g. by telephone. An adjustable highpass filter is inserted right after a microphone preamplifier, in order to remove the very lowest frequencies (adjustable limiting frequency in the range 0,5-20 Hz). Thus, the sound frequencies reproduced in this case are shifted, and must be re-interpreted by the listener.
From U.S. Pat. No. 4,731,849 is known an electronic stethoscope having a microphone, a preamplifier, automatic gain control and bandpass filtering before end amplification to a head set/loudspeaker. In this case the bandpass filter section comprises ten parallel bandpass filters, however, all these filters operate simultaneously to transmit ten selected/pre-set frequency ranges with about the same bandwidth. The output from each filter can be attenuated to zero according to wish, so that one has available ten fixed, selectable ranges which can be used separately or in combination. Thus, this arrangement provides certain options regarding choice of listening range, but is nevertheless a restricted system in this regard. The bandwidth is permanent for each respective one of the filters.
About the same options for varying the listening frequency range is provided in German Offenlegungsschrift DE 41 00 607, which publication also exhibits an electronic stethoscope having various filters which can be switched in and have different filter characteristics, inter alia bandpass characteristics.
However, none of the previously known devices seem to give to the doctor who shall prepare the diagnosis, complete and free options for selecting which frequency range shall be used, i.e. possibilities for deciding freely and immediately which part of the sound spectrum should form the basis of the analysis, without regard to whether the sound shall be listened to or recorded in some other manner.
The present invention has been conceived just to provide such possibilities, and this is achieved in accordance with the invention by providing an apparatus of the type as defined in patent claim 1.
Further embodiments of the invention are defined in the attached dependent patent claims.